1. Technical Field
This application generally relates to data storage, and more particularly to techniques used in connection with environments having different device geometries.
2. Description of Related Art
Computer systems may include different resources used by one or more host processors. Resources and host processors in a computer system may be interconnected by one or more communication connections. These resources may include, for example, data storage devices such as those included in the data storage systems manufactured by EMC Corporation. These data storage systems may be coupled to one or more host processors and provide storage services to each host processor. Multiple data storage systems from one or more different vendors may be connected and may provide common data storage for one or more host processors in a computer system.
A host processor may perform a variety of data processing tasks and operations using the data storage system. For example, a host processor may perform basic system I/O operations in connection with data requests, such as data read and write operations.
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units, disk drives, and disk interface units. Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units; also referred to as logical devices or logical volumes, may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
A device, such as a logical device described above, has a size or capacity that may be expressed in terms of device geometry. The device geometry may be obtained using SCSI commands such as the mode sense page 3 and page 4 commands and the read capacity command. The device geometry may include device geometry parameters regarding the number of cylinders in the device, the number of heads or tracks per cylinder, and the number of blocks per track. The device capacity expressed in blocks may be represented as a mathematical product of the foregoing parameters. Each of the logical devices may be further divided into one or more partitions. Each logical device partition may be defined in a partition definition structure in terms of values affected by the device geometry parameters. For example, a partition may be defined as having a start cylinder and an end cylinder. The device geometry of the data storage system upon which the device is configured and the partition definition structure may be stored in a logical device descriptor or label.
Data from a first device in a first data storage system having a first geometry may be copied to a second device in a second data storage system having a second geometry different than the first geometry. Stored in the second device's descriptor is information indicating geometry parameters of the first data storage system. A problem may arise when performing an operation to add, delete, or modify an existing partition on the second device resulting in a modification to the partition definition structure of the device descriptor on the second device. When performing such an operation to update the partition information, a discrepancy exists between the device geometry parameters as stored in the second device's descriptor (e.g., reflecting those in accordance with the first data storage system) and the device geometry parameters of the second device as reported by the second data storage system. Existing techniques detecting the foregoing discrepancy may presume that there has been data corruption to the second device's descriptor resulting in subsequent processing that may be undesirable, such as ignoring the data included in the second device's descriptor and/or reinitializing the second device's descriptor.